Preparation of unsaturated monoesters by catalytic oxidative carbonylation of diolefins

ABSTRACT

A process for the preparation of an unsaturated monoester having the formula ##STR1## wherein R is an alkyl group of from 1 to 4 carbon atoms and R&#39; is hydrogen or a methyl group which comprises reacting carbon monoxide and oxygen with a diolefin having the formula ##STR2## wherein R&#39; is as hereinabove described, in the presence of a catalytic amount of a platinum group metal compound, a copper or iron oxidant salt compound and a stoichiometric amount of a dehydrating agent. 
     Alternatively, a ligand or coordination complex compound of the metal salt compound, and catalytic quantities of an alcohol may be employed.

BACKGROUND OF THE INVENTION

The oxidative carbonylation of mono-olefins such as ethylene andpropylene to prepare carboxylic acids and derivatives employing variouscatalyst systems, particularly noble metal catalysts is known; see forexample, Fenton and Steinwand, Journal of Organic Chemistry, Vol. 37,2034 (1972) as well as U.S. Pat. Nos. 3,397,226; 3,876,694; 3,907,882,3,923,883; and 3,960,934.

In an article by Jiro Tsuji, Accounts of Chemical Research, Vol. 2, 144,(1969) and bibliographic references (36) and (37) noted therein, thecarbonylation of butadiene-isoprene-palladium chloride complexes inalcohol to give 1,4-dichloro-2-butene and ethyl 3-pentenoate and ethyl5-ethoxy-3-methyl-3-pentenoate and dimethylbutyrolactone, with otherminor products is described. In a related article by S. Hosaka and J.Tsuji, Tetrahedron, Vol. 27, 3821-3829 (1971) the palladium catalyzedcarbonylation in alcohol of various conjugated dienes and the reactionmechanism are shown.

A recent Japanese Kokai Pat. No. 75,130714, Oct. 16, 1975, describes thepreparation of carboxylic acid esters by reacting conjugated dienes,carbon monoxide and at least stoichiometric amounts and generally anexcess of an monohydric alcohol in the presence of molecular oxygen anda Group 8 noble metal catalyst. Dehydrating agents may be used ifnecessary to maintain non-aqueous conditions.

While oxidative carbonylation reactions are generally known, the priorart does not show or describe the process of the present invention forthe oxidative carbonylation of a diolefin, such as butadiene, toselectively prepare an unsaturated monoester employing stoichiometricamounts of reactant dehydrating agent compound which monoester may befurther processed by catalytic dimerization, catalytic hydrogenation andcatalyzed hydrolysis reaction sequences to prepare pelargonic andsebacic acid and related derivatives including useful difunctionalmonomers. Catalytic dimerization of the monoester, methylpenta-2,4-dienoate, can provide fatty acid precursors. The dienemonoesters of the instant invention are especially useful asdifunctional monomers for the preparation of speciality block, graft,and other polymers.

The process of the present invention is directed to the preparation of adiene monoester by the catalytic oxidative carbonylation of a diolefin.More particularly, the instant process relates to the synthesis ofmonoesters by reacting carbon monoxide, oxygen and a diolefin such as1,3-butadiene, isoprene, chloroprene, 2,3-dimethylbutadiene,1,3-pentadiene and the like, under elevated temperature and pressureconditions in the presence of a catalytic amount of a ruthenium,rhodium, palladium, osmium, iridium or platinum metal salt compound ormixtures thereof, a copper (I), copper (II), iron (II) or iron (III)oxidant salt compound and a stoichiometric amount of a reactantdehydrating agent which may be, for example, an orthoester, ketal,acetal, or trialkyl orthoborate. Co-catalytic ligands or coordinationcomplex compounds of the metal salt compounds and catalytic quantitiesof a primary, secondary or tertiary saturated alcohol while not requiredin the process of the invention, may also be employed.

The process of this invention provides an economic process for theselective preparation of a diene monoester, which may be a monobasicfatty acid or sebacic acid precursor, by the oxidative carbonylation ofa conjugated diolefin such as butadiene. There is provided a goodconversion of the diolefin employed, especially 1,3-butadiene, andexcellent yield selectivity to the diene monoester. Carbonate esters,oxalate esters, carbon dioxide as well as other side reaction productsassociated with the oxidative carbonylation reaction are obtained inonly trace amounts or eliminated by the reaction conditions employed incarrying out the process of the invention. The reaction is catalytic inboth the platinum group metal salt compound and oxidant salt compoundand employs at least stoichiometric quantities of reactant diolefins,carbon monoxide, oxygen and/or air, and dehydrating agent. The reactioncan be safely and conveniently carried out under a non-explosive oxygenor air/carbon monoxide atmosphere.

SUMMARY OF THE INVENTION

According to the present invention diolefins are oxidativelycarbonylated with carbon monoxide and oxygen or an oxygen-containing gasin the presence of a platinum group metal compound such as a palladiumhalide, a copper or iron oxidant salt compound such as a copper (I)iodide and a stoichiometric amount of a dehydrating agent such asdimethoxycyclohexane to produce a diene monoester. The process iscarried out at suitable temperatures and pressures and alternativelycontemplates the use of catalytic quantities of an aliphatic, alicyclicor aralkyl alcohol and the use of catalytic amounts of various ligands,which will not work in themselves, in conjunction with the platinumgroup metal salt compound and the oxidant salt.

It is a primary object of this invention to provide a process for thepreparation of diene monoesters in high yield and good conversion ofreactants which esters may be further processed to pelargonic, otherfatty acids and sebacic acid derivatives.

It is another object of the invention to provide a novel reaction systemfor the conversion of carbon monoxide, oxygen and diolefins to dienemonoesters.

It is a further object of this invention to provide a specific catalyticmechanism for the employment of platinum group metal compounds, oxidantsalt compounds and dehydrating agents in an oxidative carbonylationprocess employing a diolefin.

These and other objects and advantages of this invention will becomeapparent from the description of the invention which follows and fromthe claims.

DESCRIPTION OF THE INVENTION

In accordance with this invention, a diene monoester having the formula##STR3## wherein R and R' are as hereinafter described, is produced byreacting, under liquid phase conditions, a mixture of carbon monoxideand oxygen or an oxygen-containing gas with a diolefin, at elevatedtemperatures and pressures in the presence of a catalyst systemcomprising (1) a platinum group metal or platinum group metal compoundor mixtures thereof, with or without a ligand or coordination complexcompound such as lithium iodide and (2) a catalytic amount of a copper(I), copper (II), iron (II) or iron (III) metal oxidant salt compound.In addition, a stoichiometric quantity of a suitable dehydrating agent,based on the diolefin being reacted, is employed in the reaction inorder to essentially avoid the problems associated with the presence ofwater in the system which is produced therein by the oxidant-reoxidationreaction. While not essential to the oxidative carbonylation of thediolefin as set forth herein, a catalytic amount of an alcoholespecially an aliphate alcohol, is preferably employed in the reactionto aid in initiating the oxidative carbonylation reaction. The reactantsare initially charged in an essentially anhydrous condition.

A general postulated equation for the reaction of the present inventionmay for example be represented as follows: ##STR4## wherein R is analkyl group of from 1 to 4 carbon atoms or an aralkyl group containing 6carbon atoms in the ring and from 1 to 4 carbon atoms in the alkylsubstituent, and R' is hydrogen, a halogen, an alkyl group of from 1 to4 carbon atoms or an alkyl group containing 6 carbon atoms in the ring.

The reaction between the diolefin, carbon monoxide, oxygen, anddehydrating agent may be carried out in an autoclave or any otherappropriate reactor. Although the order of addition of reactants andcatalyst components may vary, a general procedure is to charge thediolefins, dehydrating agent, platinum group metal compound, oxidantsalt compound into the reaction vessel, and if desired a ligand orcoordination complex compound and a catalytic quantity of an alcohol,then introduce the proper amount of carbon monoxide and oxygen to thedesired reaction pressure and then heat the mixture to the desiredtemperature for the appropriate period. The reaction can be carried outbatchwise or as a continuous process and the order of addition ofreactants and catalyst may be varied to suit the particular apparatusemployed. The addition of the oxygen or oxygencontaining gas, such asair, can be a pulsed or continuous addition to the reaction system. Thereaction products are recovered and treated by any conventional methodsuch as distillation and/or filtration, etc. to effect separation of themonoesters from unreacted materials, platinum group metal salt compound,oxidant salt compound, by products, including for example, when reacting1,3-butadiene, dimethyl hex-3-endioate, dimethyl hex-2,4-diendioate,methylpent-3-enoate, methyl 3-methoxypent-4-enoate, methyl5-methoxypent-3-enoate, methyl nonadilnoates, dimethl decadiendioates,dimethyl oxalate, and CO₂, etc. Catalysts, including solvents which mayhave been employed, may be recycled to the system.

The diolefins which may be employed in concentrations of from about 10to 80 weight percent, preferably 20 60 weight percent, or on astoichiometric molar basis with the dehydrating agent employed, andsuitable for use in the process of the present invention conform to thegeneral formula ##STR5## wherein R' which may be the same or different,is hydrogen, a halogen, an alkyl group of from 1 to 4 carbon atoms or anaryl group containing 6 carbon atoms in the ring. Representativediolefins within the above noted formula include for example, butadiene,isoprene, chloroprene, 2,3-dimethyl-, 2,3-diethyl-, 2,3-dipropyl, and2,3-dibutylbutadiene, 1,3- and 2,4-heptadienes, 1,3-pentadiene,piperylene, 2-ethyl-1,3-butadiene, 1-phenylbutadiene,1,4-diphenylbutadiene, 2,-chloro-3-methylbutadiene, 1-chlorobutadiene,2,5-dimethyl-2,4-hexadiene, 2-bromobutadiene, 2-iodobutadiene,2-chloro-1-phenylbutadiene, etc. Butadiene and isoprene are thepreferred diolefins and butadiene is most preferred.

Suitable dehydrating agents which may be employed and in at leaststoichiometric amounts in the process of the invention include, forexample, acetals, ketals, carboxylic orthoesters, trialkylorthoboratesand dialkoxycycloalkanes.

The acetals and ketals suitable for use in the process of the presentinvention conform to the general formulae: ##STR6## respectively. R maybe a substituted or unsubstituted alkyl group containing from 1 to 20carbon atoms preferably 1 to 10 carbon atoms. R may also be asubstituted or unsubstituted alicyclic, or an aryl group containing oneor more benzenoid rings preferably not more than 3 rings which may befused or joined by single valency bonds. R' and R" which may be the sameof different may be a substituted or unsubstituted alkyl groupcontaining from 1 to 8 carbon atoms preferably 1 to 4 carbons in thealkyl chain or an aralkyl group containing 6 carbon atoms in the ringand from 1 to 4 carbon atoms in the alkyl substituent. R, R' and R" maycontain substituents such as amido, alkoxy, amino, carboxy, cyano, etc.radicals. Representative acetals suitable for use in this inventioninclude, for example, the 1,1-dialkoxyalkanes such as dimethoxymethane,dibutoxymethane, 1,1-dimethoxyethane, 1,1-dimethoxypropane, ethyldiethoxyacetate, 1,1,2-trimethoxyethane, 1,1-dimethoxy-2-propene, anddimethoxy- and diethoxyphenylmethane, etc. In a like manner for examplethe acetals 1-methoxy-, 1-ethoxy- and 1-propoxytetrahydrofuran,2,5-diethoxytetrahydrofuran, and 2-ethoxy-4-methyl-3,4-dihydro-2H-pyranetc. may be employed. Representative ketals suitable for use in thisinvention include for example, 2,2-dimethoxy-, 2,2-diethoxy- and2,2-dipropoxypropane, butane, pentane, etc. 3,3-dimethoxy- and3,3-diethoxy-1-pentene, 1-butene, etc., 1,1-dimethoxycyclohexane,1,1-diethoxycyclohexane, 1,1-dibutoxycyclohexane, etc.,1,1-dibutoxy-4-methylcyclohexane,1,1-dimethoxy-1,2,3,4-tetrahydronaphthalene, etc. and1,1-bis(2-propenoxy)cyclohexane.

The carboxylic ortho esters suitable for use in the process of theinvention conform to the general formula ##STR7## wherein R may behydrogen or a substituted or unsubstituted alkyl group containing from 1to 20 carbon atoms preferably 1 to 10 carbon atoms. R may also be analicyclic, or an aryl group containing one or more benzenoid ringspreferably not more than 3 rings which may be fused or joined by singlevalency bonds. R', R" and R'" which may be the same or different may besubstituted or unsubstituted alkyl groups containing from 1 to 8 carbonatoms preferably 1 to 4 carbon atoms in the alkyl chain or an aralkylgroup containing 6 carbon atoms in the ring and from 1 to 4 carbon atomsin the alkyl substituent. R, R', R", and R'" may contain substituentssuch as amido, alkoxy, amino, carboxy, cyano, etc. Representativecarboxylic ortho esters suitable for use in this invention include, forexample, trimethyl orthoformate, triethyl orthoformate, triphenylorthoformate, tri-n-propyl orthoformate, etc., triethyl tripropyl,tributyl, trimethyl orthoacetate, etc., trimethyl, triethyl, tripropyl,tributylorthopropionate, etc., trimethyl, triethyl, tripropyl, tributylorthobutyrate, etc., trimethyl, triethyl, tripropyl, tributyl,orthoisobutyrate, etc., trimethyl, triethyl, tripropyl, tributylorthocyanoacetate, etc., trimethyl triethyl, tripropyl, tributylorthophenylacetate, etc., trimethyl, triethyl, tripropyl, tributylortho-α-chloroacetate, etc., trimethyl, triethyl, tripropyl, tributylortho-α-bromoacetate, etc., trimethyl, triethyl, tripropyl, tributylorthobenzoate, etc., trimethyl, triethyl, tripropyl, tributylortho-p-chlorobenzoate, etc., hexamethyl-p-diorthophthalate, etc., ethyltriethoxyacetate, hexaethyl orthooxalate, triethyl ortho-3-butynoate,etc. In a like manner the esters trimethyl, triethyl, tripropylorthocarbonate, 2-isopropyl-2-methoxy-1,3-dioxolane,2-methyl-2-ethoxy-1,3-dioxolane, 2,2-diethoxytetrahydrofuran,2,2-diethoxychroman, 1,4,5-trioxaspiro[4,4]nonane,2,6,7-trioxabicyclo[2,2,2]octanes,2,4,10-trioxaadamantane-2,4,10-trioxatricyclo[3,3,1,13,7]decane may beemployed.

The orthoborate esters employed in at least stoichiometric quantitiesand suitable for use in the process of the present invention arepreferably symmetrical and conform to the general formula ##STR8##wherein R is a substituted or unsubstituted alkyl group containing from1 to 8 carbon atoms in the alkyl chain or an aralkyl group containing 6carbon atoms in the ring and from 1 to 4 carbon atoms in the alkylsubstituent. Particularly preferred are the orthoborates wherein each Ris a straight chain alkyl group containing from 1 to 4 carbon atoms suchas triethyl borate. Representative ortho borate esters suitable for usein this invention include, for example, trimethylborate, triethylborate,tri-2-chloroethyl borate, tritolyl borates, tri-methoxybenzyl borates,tri-chlorobenzyl borates, tri-benzyl borate, tri-4-butylphenyl borate,tri-n-propyl and tri-isopropyl borates, tri-(1,3-dichloro-2-propyl)borate, tri-n-butyl, tri-s-butyl and tri-t-butyl borates,tri-(β,β,β-trichloro-t-butyl)borate, triphenyl borate,tri-o-chlorophenyl borate, tri-n-amyl borate, tri-t-amyl borate,tri-(o-phenylphenyl) borate, tri-n-hexyl borate, tri-3-heptyl borate,tri-3-pentyl borate, tri-n-octyl and tri-isooctyl borates,tri-(2-ethylhexyl)borate, tri-(methylisobutylcarbonyl) borate,tri(diisobutylcarbinyl) borate, tri-(2,5-dimethylbenzyl) borate, etc.

The dialkoxycycloalkanes, which are the preferred dehydrating agents foruse in the present invention, in at least stoichiometric quantities,conform to the general formula ##STR9## wherein R is a substituted orunsubstituted alkyl group containing from 1 to 4 carbon atoms and x isan integer of from 4 to 9. R may contain substituents such as amido,alkoxy, amino, carboxy, cyano, etc. radicals. In addition, the cyclicring may be substituted with alkyl groups of up to 4 carbon atoms.Dimethoxycyclohexane is the most preferred. Representativedialkoxycycloalkanes include for example, dimethoxy-, diethoxy-,dipropoxy- and dibutoxycyclopentanes, and the corresponding dimethoxy,diethoxy, dipropoxy and dibutyoxycyclohexanes, heptanes, octanes,nonanes and decanes, as well as 4-ethyl-1,1-dimethoxycyclohexane, etc. Ageneral postulated equation for the reaction using dimethoxycyclohexanein the oxidative carbonylation of butadiene may be represented asfollows: ##STR10##

The platinum group metal compounds which may be employed in the processof this invention as catalyst are the palladium, platinum, rhodium,ruthenium, iridium, and osmium salts or mixtures thereof. Among thechemical forms of the platinum group metal salt compounds which can beused as such or as mixtures or formed in the reaction system from themetals per se are, for example, the palladium, platinum, rhodium,ruthenium, iridium and osmium, halides, sulfates, nitrates, oxides,oxalates, acetates and trifluroacetates, preferably the palladium (II)halides, particularly palladium (II) iodide. Representative catalyticplatinum group metal salt compounds include, for example palladium (II)iodide, π-allyl palladium iodide, platinum (II) iodide, rhodium (III)iodide, ruthenium (III) iodide, palladium (II) sulfate, palladium (II)acetate, palladium (II) trifluoroacetate, palladium (II) bromide,rhodium (III) bromide, iridium (III) chloride, platinum (II) sulfate,osmium (II) chloride, palladium (II) oxide, osmium tetroxide, iridium(III) sulfate, etc. As indicated above the metals as such may be addedto the reaction as part of the catalyst mixture, the salt compound beingformed in situ from at least a portion of the platinum group metal underreaction conditions.

The palladium, platinum, rhodium, ruthenium, osmium and iridiumcompounds employed may be in a homogeneous state in the reaction mixtureat reaction conditions. Thus, the compounds may be present in solution,or suspension and may also be on support materials such as alumina,silica gel, aluminosilicates, activated carbon or zeolites or may beanchored to a polymer support. The compounds may be partially orcompletely soluble under reaction conditions. The reaction is generallycarried out in the presence of a catalytic proportion of the platinumgroup metal salt compound and will proceed with small amounts of themetal salt compounds hereinabove described. Generally the proportions ofthe platinum group metal salt compound used in the reaction will beequivalent to between about 0.001 to 5 weight percent of the diolefinemployed and are preferably employed in amounts between about 0.01 to 2percent by weight of the diolefin employed. Larger or smaller amountsmay be employed at varied pressures and temperatures.

As mentioned hereinabove, alternatively, a ligand or coordinationcomplex compound of the platinum group metal salt compound may beemployed in the process of the invention as co-catalyst in the catalyticmixture and thereby also achieve a pronounced increase in theselectivity for the diene monoester. The ligands may be, for example,alkyl or aryl phosphines, arsines, or stibines or salts of the alkalimetals, e.g., lithium, sodium, potassium, rubidium, cesium salts, suchas lithium bromide, sodium iodide, potassium iodide, lithium acetate,lithium iodide, etc. The complexes of the metal salt compounds which aresuitable for use in the process of the present invention include complexcompounds of palladium, platinum, rhodium, ruthenium, osmium andiridium. The complex compounds may contain one or more atoms of the saltmetals in the molecule and when more than one such atom is present, themetals may be the same or different. The mono- or polydentate ligandswhich are present in the molecule of the complex compounds and in whichat least one of the electron-donating atoms is an atom of phosphorus,arsenic or antimony or a halide ion containing a lone pair of electronsmay be, for example, organo-phosphines, -arsines and -stibines and theiroxides. Suitable monodentate ligands include alkyl phosphines such astrimethylphosphine and tributylphosphine, arylphosphines such asdiethylphenylphosphine and radicals derived from such phosphines, forexample the radical having the formula --P(CH₃)₂. Hydrocarbyloxyphosphines, i.e., phosphites, such as triphenyl phosphite may also beemployed. Suitable polydenate ligands include tetramethyldiphosphinoethane and tetraphenyl diphosphinoethane. Exactly analogousderivatives of arsenic and antimony may be used; however, because oftheir greater ease of preparation and stability of the derivedcomplexes, the hydrocarbyl derivatives of phosphorus are preferred. Itis preferred to employ the alkali metal halides, particularly thelithium halides such as lithium bromide and lithium iodide.

Benzonitrile, acetonitrile, isocyanates, isothiocyanates, pyridine,pyridyls, pyrimidine, quinoline, isoquinoline may also serve as suitableligands to modify the platinum group metal catalyst activity or catalystsolubility.

The complex compounds suitable for use in the process of the presentinvention may contain in the molecule, in addition to the ligandsdiscussed above, one or more other atoms, groups or molecules, which arechemically bonded to the metal atom or atoms. Atoms which may be bondedto the metal include, for example, hydrogen, nitrogen, and halogenatoms; groups which may be bonded to the metal include, for examplehydrocarbyl, hydrocarbyloxy, carbonyl, nitrosyl, cyano and SnCl₃ --groups; molecules which may be bonded to the metal include, for exampleorganic isocyanides and isothiocyanates. Examples of suitable complexcompounds are those represented by the following formulae:

    ______________________________________                                        RhBr.sub.3 (PPhEt.sub.2).sub.3                                                                   Rh(CO)Cl(AsEt.sub.3).sub.2                                 Rh I (CO) (PPhEt.sub.2).sub.2                                                                    RhCl(CO) (PEt.sub.3).sub.2                                 Rh(Ph.sub.2 PCH.sub.2 CH.sub.2 PPh.sub.2).sub.2 I                                                PdBr.sub.2 (PPh.sub.3).sub.2                               Rh[(PhO).sub.3 P].sub.3 I                                                                        PdI.sub.2 (PPh.sub.3).sub.2                                Li.sub.2 PdI.sub.4 PtCl.sub.2 (p-ClC.sub.6 H.sub.4 PBu.sub.2).sub.2           (PhCN).sub.2 PdI.sub.2                                                        ______________________________________                                    

The complex compounds employed may be introduced into the reactionmixture as such, or they may be formed in situ from a suitable platinumgroup metal or metal compound noted above and the desired ligand.

The ligand or complex compounds may be used in catalytic amounts of from0 to 3 percent preferably from 0.1 to 1 percent by weight of thediolefin to be reacted although larger or smaller amounts may beemployed at varied pressures or reaction rates.

The oxidant salt compounds which may be employed in an essentiallyanhydrous condition in the process of the present invention and incatalytic amounts of from 0.1 to 10 weight percent preferably 0.50 to 6weight percent include the iron (II), iron (III), copper (I) and copper(II) salts such as the halides, sulfates, trifluoroacetates, nitrates,oxalates, naphthanates, hex-3-endioates or acetates and preferablycopper (I) iodide and iron (II) iodide. Representative oxidant saltsinclude, for example, copper (II) sulfate, copper (II) trifluoroacetate,copper (II) acetate, copper (II) oxalate, copper (II) triflate, copper(II) fluorosulfonate, copper (I) bromide, copper (I) sulfate, iron (III)sulfate iron (II) bromide, iron (II) chloride, iron (III) acetate, iron(III) oxalate, copper (II) penta-2,4-dienoate, iron (II)penta-2,4-dienoate and iron (III) trifluoroacetate.

While not necessary to the reaction of the present invention, it isoften desirable to add a small amount of an acid to aid in initiatingthe reoxidation (by oxygen) of copper (I) to copper (II) or iron (II) toiron (III). Suitable acids include for example hydroiodic, hydrobromic,sulfuric, phosphoric and acetic in concentrations of from 0-2 weightpercent of diolefin.

As indicated hereinabove, an alcohol in catalytic quantities may beemployed in the process of the invention primarily to aid in initiatingthe oxidative carbonylation reaction. The alcohols may be employed inconcentrations of from 0 to 20 and preferably 0.5 to 10 weight percentof the diolefin employed. The alcohols may be saturated monohydricprimary, secondary or tertiary alcohols and conform to the generalformula ROH, wherein R is an optionally substituted aliphatic oralicyclic group containing from 1 to 20 carbon atoms and preferably theunsubstituted aliphatic alcohols containing from 1 to 8 carbon atoms. Rmay also be a substituted or an unsubstituted aralkyl group. In general,the substituents which may be amido, alkoxy, amino, carboxy, etc.radicals, in addition to the hydroxyl group, do not interfere with thereaction of the invention. Representative alcohols especially suitablefor use in this invention are saturated monohydric alcohols such asmethyl, ethyl, n-, iso-, sec-, and tert-butyl, amyl, hexyl, octyl,lauryl, n- and isopropyl, cetyl, benzyl, chlorobenzyl and methoxybenzylalcohols as well as, for example, tolylcarbinol, cyclohexanol,heptanols, decanols, undecanols, 2-ethyl hexanol, nonanol, myristylalcohol, stearyl alcohol, methyl cyclohexanol, pentadecanol, oleyl andeicosonyl alcohols, and the like. The preferred alcohols are the primaryand secondary monohydric saturated aliphatic alcohols, such as methanol,ethanol, 1- and 2-propanol, n-butyl alcohol, etc., up to 8 carbon atoms.The R group of the alcohol may be different from the R groups of thedehydrating agents noted hereinabove, resulting in the preparation ofmixed diene esters.

Solvents, if desired, which are chemically inert to the components ofthe reaction system may be employed, and in some cases, especially inthe oxidative carbonylation of 1,3-butadiene, will improve theselectivity and conversion to the diene monoester as well as thecatalyst solubility or boiling point range for product and catalystrecovery. Suitable solvents include for example, dioxane,dimethylcarbonate, dimethyladipate, benzene, nitrobenzene, acetonitrile,tetrahydrofuran, methyl acetate, ethyl acetate, isopropyl acetate,n-propyl formate, butyl acetates, cyclohexyl acetate, n-propyl benzoate,lower alkyl phthalates, etc. the alkyl sulfones and sulfoxides such aspropyl ethyl sulfoxide, diisopropyl sulfone, diisooctyl sulfoxide,acetone, cyclohexanone, methyl formate, etc.

The process of the present invention can be suitably performed byintroducing the oxygen and carbon monoxide at a desired pressure intocontact with the diolefin, dehydrating agent, the platinum group metalsalt compound and the copper or iron oxidant salt and possibly acatalytic amount of an alcohol as well as a cocatalytic amount of aligand or coordination complex and heating to the desired temperature.In general, a carbon monoxide pressure of about 15 psig to about 5000psig partial pressure and preferably from 100 psig to about 2000 psig isemployed. Stoichiometric quantities of carbon monoxide are generallyemployed. However, an excess of carbon monoxide may be employed, forexample, in continuous processes where a large excess of or high carbonmonoxide requirements are generally utilized, a suitable recycle of theunreacted carbon monoxide may be employed. The reaction will proceed attemperatures of from about 25° C. to 200° C. It is generally preferredto operate the process at temperatures in the range of 80° C. to 150° C.to obtain a convenient rate of reaction with the particular diolefin.Lower temperatures may be employed but the reaction rate is slower.Higher temperatures may also be used depending on the diolefin to bereacted. At the higher temperatures the diolefin employed may be in thevapor state. Heating and/or cooling means may be employed interiorand/or exterior of the reaction to maintain the temperature within thedesired range.

At least stoichiometric amounts of oxygen or an oxygen-containing gassuch as air may be employed and at any oxygen partial pressure such thatthe explosive range is avoided. Thus, the concentrations of oxygenshould be low enough so that the reaction mixture is not potentiallyexplosive. The Handbook of Chemistry and Physics, 48th Edition, 1967indicates that the explosive limits of pure oxygen in carbon monoxide is6.1 to 84.5 volume percent and air in carbon monoxide to be 25.8 to 87.5volume percent.

The reaction time is generally dependent upon the diolefin beingreacted, temperature, pressure and on the amount and type of thecatalyst, oxidant and dehydrating agent being charged as well as thetype of equipment being employed. Reaction times will vary dependent onwhether the process is continuous or batch and may vary from 10 to 600minutes. Reaction time for butadiene is generally about 120 minutes.

The following examples are provided to illustrate the invention inaccordance with the principles of this invention but are not to beconstrued as limiting the invention in any way except as indicated bythe appended claims.

Although the process of the present invention will primarily be directedto the oxidative carbonylation of 1,3-butadiene to produce the dienemonoester, methyl penta-2,4-dienoate, which is an important precursorfor the preparation of pelargonic and sebacic acid, it is not intendedthat the process be limited to the butadiene type diolefins and thoseskilled in the art will recognize that the present invention is broadlyapplicable to the oxidative carbonylation of other conjugated diolefins,within the formula as hereinabove set forth, to produce otherunsaturated monoester products such as a 1,3-pentadiene to methyl2-methylpenta-2,4-dienoate.

In the examples which follow the reactions were carried out in a 500 ml.nickel-molybdenum (HASTELLOY Alloy) stirred autoclave or 500 ml.titanium lined stirred autoclave. The liquid feed and solid catalystcomponents were charged into the autoclave as homogeneous solutionswhere possible. The diolefins were charged into a sight glass andallowed to come to thermal equilibrium before being charged into theautoclave as a liquid under pressure. Carbon monoxide was charged intothe autoclave to the desired pressure followed by heating to the desiredreaction temperature. Total system pressure was adjusted to the desiredlevel by the addition of more carbon monoxide. Oxygen or air was addedand a non-explosive carbon monoxide/oxygen gas mixture maintained. Whereoxygen was employed, carbon monoxide was pulsed into the autoclave tosweep the oxygen out of the pressure tubing. Cooling water wascirculated through the internal autoclave cooling coils to maintain thedesired reaction temperature and to control the reaction exothermobserved upon the addition of reactant oxygen. After each gas uptakelevelled out, total system pressure was readjusted and additional oxygenadded. The procedure of charging oxygen or air increments and sweepingout the pressure lines with CO was repeated until no more gas uptake wasobserved or for the desired reaction time.

Upon completion of the reaction, the reactor was cooled to ambienttemperature and vented to ambient pressure and gas samples obtained.Solids were separated from liquids by vacuum filtration. The gaseousproduct volume was measured and analyzed by mass spectral analysis (MS)and the liquid product was analyzed by gas-liquid chromatography (glc).Material balances on the diolefins were obtained by considering the MSand glc results.

Diolefin conversions were calculated on the basis of moles of diolefinconsumed by the reaction. Product selectivities were based on themillimoles of diolefin required to make the monoester and by-products.The amount of unreacted diolefin was obtained by MS analysis of thegases and glc analysis for diolefin in the liquid product.

EXAMPLES 1 to 3

In Examples 1 to 3 a solution of alcohol and dehydrating agent wascharged into the autoclave along with 1.51 g. (4.2 mmole) palladium (II)iodide, 1.98 g. (10.4 mmole) copper (I) iodide and 1.12 g. (8.4 mmole)lithium iodide. 1,3-butadiene was charged into the autoclave as a liquidunder pressure. The reaction temperature was 100° C. and the totalinitial carbon monoxide pressure was 900 psig. The reaction wasinitiated by a 50 psig charge of oxygen and 50 psig line purging chargeof carbon monoxide giving a total system pressure of 1000 psig. A strongexotherm and pressure drop of 75-100 psig over a course of 20 minuteswas observed. The oxygen cycle was repeated five more times inincrements of 25 psig oxygen and 50 psig carbon monoxide at intervals of20 minutes during an autoclave residence period of 120 minutes. A totalpressure drop of about 600 psig was observed. The reaction wasterminated before completion and cooled to ambient temperature. Thealcohol and dehydrating agents and amount of 1,3-butadiene employed andanalytical results giving the conversion and selectivities to the methylpenta-2,4-dienoate is shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                                          1,3-                                                                          Bu-                                                                           tadi-                                                                         ene  Ester                                       1,3-                Dehy-    Con- Selectivity                                 butadiene           dration.sup.(1)                                                                        ver- Based                                       Charged   Alcohol.sup.(2)                                                                         Agent    sion on 1,3-                                Ex.  g. (mmoles)                                                                             (mmole)   (mmole)  (%)  Butadiene                              ______________________________________                                        1    27 g. (500)                                                                             MeOH (32) DMOC (500)                                                                             15   81 mole %                              2    54 g. (1000)                                                                            MeOH (32) TMOF (1000)                                                                            11   81 mole %                              3    54 g. (1000)                                                                            MeOH (32) DMP (1000)                                                                             12   80 mole %                              ______________________________________                                         .sup.(1) DMOC  1,1dimethoxycyclohexane                                        TMOF  trimethylorthoformate                                                   DMP  2,2dimethoxypropane                                                      .sup.(2) MeOH  methyl alcohol                                            

EXAMPLES 4 to 13

In Examples 4 to 13 the procedures and conditions, except as noted forExamples 12 and 13, of Examples 1 to 3 were repeated to oxidativelycarbonylate 1,3-butadiene employing 0.66 g. (2.5 mmole) palladium (II)bromide, 2.86 g. (15 mmole) copper (I) iodide and 0.67 g. (5 mmole)lithium iodide. In Example 12 the initial carbon monoxide pressure was100 psig, the reactor was heated to 100° C. and the carbon monoxidepressure adjusted to 375 psig. The reaction was initiated by a 25 psigcharge of oxygen and a 50 psig line flushing charge of carbon monoxidegiving a total system pressure of 450 psig. A strong exotherm andpressure drop was noted. When the pressure dropped below 375 psig it wasreadjusted by adding increments of 25 psig oxygen followed by 50 psigCO. The reaction was carried out for 120 minutes, i.e., prior tocompletion. In Example 13 the procedure of Example 12 was followed withall pressure doubled giving a total system pressure of 900 psig. Thealcohol, dehydrating agent and amount of 1,3-butadiene employed as wellas the analytical results for Examples 4 to 13 giving selectivities andconversions to the methyl, ethyl or butyl methyl penta-2,4-dienoate isshown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                              1,3-  Ester                                             1,3-butadiene         Butadiene                                                                           Selectivity                                       Charged                                                                              Alcohol.sup.(4)                                                                      Dehydration.sup.(1)                                                                   Conversion                                                                          Based on 1,3-                                 Ex. g. (mmoles)                                                                          (mmole)                                                                              Agent (mmole)                                                                         (%)   Butadiene                                     __________________________________________________________________________     4  27 g. (500)                                                                          MeOH (32)                                                                            DMOC (500)                                                                            18    74 mole %                                      5  54 g. (1000)                                                                         MeOH (32)                                                                            DMOC (1000)                                                                           15    83 mole %                                      6  54 g. (1000)                                                                         EtOH (25)                                                                            DEOC (1000)                                                                           11    80 mole %                                      7  54 g. (1000)                                                                         BuOH (25)                                                                            DBOC (1000)                                                                           13    79 mole %                                      8  54 g. (1000)                                                                         MeOH (32)                                                                            TMOF (1000)                                                                           13    81 mole %                                      9  54 g. (1000)                                                                         MeOH (32)                                                                            TMOF (1000)                                                                           12    78 mole %                                     10  27 g. (500)                                                                          EtOH (25)                                                                            TEOF (500)                                                                            14    81 mole %                                     11  54 g. (1000)                                                                         MeOH (32)                                                                            DMP (1000)                                                                            11    82 mole %                                     12.sup.(2)                                                                        54 g. (1000)                                                                         MeOH (32)                                                                            DMP (1000)                                                                             9    85 mole %                                     13.sup.(3)                                                                        54 g. (1000)                                                                         MeOH (32)                                                                            DMP (1000)                                                                            11    83 mole %                                     __________________________________________________________________________     .sup.(1) DMOC  1,1dimethoxycyclohexane; DEOC  1,1diethoxycyclohexane; DBO      1,1dibutoxy-cyclohexane; TMOF  trimethylorthoformate; TEOF                   triethylorthoformate; and DMP  2,2dimethoxypropane                            .sup. (2) Total system pressure was 450 psig.                                 .sup.(3) Total system pressure was 900 psig.                                  .sup.(4) MeOH  Methanol; EtOH  Ethanol; BuOH  nbutanol.                  

EXAMPLES 14 to 33

In Examples 14 to 33 which follow in table form, the procedure andgeneral operating conditions of Examples 1 to 3, except as specificallynoted, were repeated using various diolefins (2 moles), dehydratingagent (1 mole), platinum group metal compound catalysts (5.0 mmoles) andoxidant salt compounds, with or without a ligand compound and catalyticalcohol. Gaseous and liquid products were analyzed by mass spectralanalysis and gas-liquid chromatography respectively.

The reaction conditions, reactants, catalysts, oxidants, alcohols andligands employed in Examples 14-33 are set forth in Table 3 and theresults showing main product, percent diolefin conversion and molepercent selectivities are summarized in Table 4.

                                      TABLE 3                                     __________________________________________________________________________           (psig)            Dehy-                                                   °C.                                                                        Pres-                                                                             Time     Alcohol                                                                            dration                                                                            (5.0 mm)                                                                            Oxidant                                                                             Ligand                              Ex.                                                                              Temp.                                                                             sure                                                                              Mins.                                                                             Diolefin                                                                           (mmole)                                                                            Agent                                                                              Catalyst                                                                            (mmole)                                                                             (mmole)                             __________________________________________________________________________    14 100 1000                                                                              120 IP.sup.(1)                                                                         --   DMOC.sup.(2)                                                                       PdCl.sub.2                                                                          CuCl.sub.2                                                                          LiCl                                15 100 1800                                                                              120 BD.sup.(3)                                                                         --   DMOC PdI.sub.2                                                                           CuI   LiI                                                                     12.5  10.0                                16 125 1800                                                                              100 BD   MeOH.sup.(4)                                                                       DMOC PtI.sub.4                                                                           CuI   LiI                                                     100             12.5  10.0                                17 125 1800                                                                              120 BD   MeOH DMOC RhI.sub.3                                                                           CuI   LiI                                                     100             12.5  10.0                                18 125 1800                                                                              120 BD   MeOH DMOC RuI.sub.3                                                                           CuI   LiI                                                     100             12.5  10.0                                19 100 1000                                                                              120 BD   MeOH DMOC PdCl.sub.2                                                                          FeI.sub.2                                                                           LiI                                                     50.0            12.5  10.0                                20 110 1000                                                                              120 BD   MeOH DMOC PdI.sub.2                                                                           CuBr.sub.2                                                                          LiBr                                                    50.0            12.5  10.0                                21 100 1800                                                                              120 BD   MeOH DMOC PdI.sub.2                                                                           CuSO.sub.4                                                                          LiI                                                     50.0            12.5  10.0                                22 110 1000                                                                              120 BD   MeOH DMOC PdI.sub.2                                                                           CuI   NaI                                                     50.0            12.5  10.0                                23 110 1000                                                                              100 BD   MeOH DMOC PdI.sub.2                                                                           CuI   KI                                                      50.0            12.5  10.0                                24 100 1800                                                                              120 BD   MeOH DMOC PdI.sub.2                                                                           CuBr  --                                                      50.0            12.5.sup.2                                25 100 1800                                                                              120 BD   MeOH DMOC PdI.sub.2                                                                           Cu(OAc).sub.2                                                                       LiI                                                     50.0            25.0  10.0                                26 100 1000                                                                              120 BD   MeOH TMOF.sup.(5)                                                                       PdI.sub.2                                                                           CuI   LiI                                                     50.0            12.5  10.0                                27 100 1000                                                                              120 BD   MeOH DMP.sup.(6)                                                                        PdI.sub.2                                                                           CuI   LiI                                                     50.0            12.5  10.0                                28 100 1800                                                                              120 BD   MeOH TMOB.sup.(7)                                                                       PdI.sub.2                                                                           CuI   LiI                                                     50.0            12.5  10.0                                29 100 1800                                                                              120 BD   MeOH TMOF PdBr.sub.2                                                                          CuI   LiI                                                     50.0            12.5  10.0                                30 100  500                                                                              120 BD   MeOH DMP  PdBr.sub.2                                                                          CuBr.sub.2                                                                          LiBr                                                    50.0            12.5  10.0                                31 100 1900                                                                              120 BD   MeOH DMOC Pd(OAc).sub.2                                                                       CuI   LiOAc                                                   50.0            25.0  10.0                                32 100 1800                                                                              180 BD   MeOH DMOC PdSO.sub.4                                                                          CuI   LiI                                                     50.0            25.0  10.0                                33 100 1800                                                                              120 BD   MeOH DMOC Pd metal                                                                            CuI   LiI                                                     50.0            25.0  20.0                                 Key                                                                           .sup.(1) IP  Isoprene                                                         .sup.(2) DMOC  1,1dimethoxycyclohexane                                        .sup.(3) BD  1,3butadiene                                                     .sup.(4) MeOH  Methyl alcohol                                                 .sup.(5) TMOF  trimethylorthoformate                                          .sup.(6) DMP  2,2dimethoxypropane                                             .sup.(7) TMOB  trimethylorthoborate                                      

                  TABLE 4                                                         ______________________________________                                                                  Di-     Mole %                                                                olefin  Ester                                                                 %       Selectivity                                                           Con-    based on                                    Ex.  Product              version 1,3-butadiene                               ______________________________________                                        14   methyl 3-methylpenta-2,4-dienoate                                                                  15      80                                          15   methyl penta-2,4-dienoate                                                                          19      81                                          16   methyl penta-2,4-dienoate                                                                           4      80                                          17   methyl penta-2,4-dienoate                                                                           8      83                                          18   methyl penta-2,4-dienoate                                                                           6      81                                          19   methyl penta-2,4-dienoate                                                                          11      81                                          20   methyl penta-2,4-dienoate                                                                          18      79                                          21   methyl penta-2,4-dienoate                                                                          16      78                                          22   methyl penta-2,4-dienoate                                                                          15      80                                          23   methyl penta-2,4-dienoate                                                                          20      83                                          24   methyl penta-2,4-dienoate                                                                          12      77                                          25   methyl penta-2,4-dienoate                                                                          14      79                                          26   methyl penta-2,4-dienoate                                                                          18      81                                          27   methyl penta-2,4-dienoate                                                                          21      79                                          28   methyl penta-2,4-dienoate                                                                           6      75                                          29   methyl penta-2,4-dienoate                                                                          19      80                                          30   methyl penta-2,4-dienoate                                                                          20      81                                          31   methyl penta-2,4-dienoate                                                                          15      82                                          32   methyl penta-2,4-dienoate                                                                          13      80                                          33   methyl penta-2,4-dienoate                                                                          17      81                                      

We claim:
 1. A process for the preparation of a diene monoester havingthe formula ##STR11## wherein R is an alkyl group of from 1 to 4 carbonatoms and R' is hydrogen or a methyl group, which comprises reacting adiolefin of the formula ##STR12## wherein R' is as above described witha mixture of carbon monoxide and oxygen and a stoichiometric amount of adehydrating agent selected from the group consisting of acetals, ketals,carboxylic orthoesters, trialkylorthoborates and1,1-dialkoxycycloalkanes, at a pressure of between about 15 psig and5000 psig and at a temperature in the range of about 25° C. to 200° C.in the presence of an effective amount of a catalytic mixture of aplatinum group metal compound selected from the group consisting ofpalladium, ruthenium, rhodium, and platinum, halides, cyanates,sulfates, nitrates, oxides, oxalates, acetates, and trifluoroacetates ormixtures thereof, an organic mono- or poly-dentate ligand orcoordination complex compound selected from the group consisting ofalkyl, aryl and halogen-substituted phosphines, arsines, stibines, andalkali metal salts, and a copper (I), copper (II), iron (II) or iron(III) oxidant salt compound and recovering the desired diene monoester.2. A process according to claim 1 wherein the diolefin is selected fromthe group consisting of 1,3-butadiene, and isoprene.
 3. A processaccording to claim 2 wherein the diolefin is 1,3-butadiene.
 4. A processaccording to claim 1 wherein the dehydrating agent is selected from thegroup consisting of 1,1-dimethoxycyclohexane, trimethylorthoformate,2,2-dimethoxypropane, trimethylorthoborate, 1,1-dimethoxyethane,1,1-diethoxypropane, 2,2-dimethoxybutane, 1,1-dibutoxycyclohexane,1,1-diethoxyhexane, and triethylorthoformate.
 5. A process according toclaim 4 wherein the dehydrating agent is 1,1-dimethoxycyclohexane.
 6. Aprocess according to claim 1 wherein the pressure is between about 100psig and 2000 psig.
 7. A process according to claim 1 wherein thetemperature is in the range of from about 80° C. to 150° C.
 8. A processaccording to claim 1 wherein the platinum group metal compound isselected from palladium (II) iodide, palladium (II) chloride, palladium(II) bromide, platinum (II) iodide, rhodium (III) iodide, ruthenium(III) iodide, palladium (II) acetate, palladium (II) sulfate, sodiumiodopalladate, sodium bromopalladate, and potassium iodopalladate, orpalladium metal.
 9. A process according to claim 8 wherein the platinumgroup metal compound is palladium (II) iodide.
 10. A process accordingto claim 8 wherein the platinum group metal compound is palladium (II)bromide.
 11. A process according to claim 1 wherein the oxidant saltcompound is selected from the group consisting of copper (I), copper(II) iron (II) and iron (III) halides, sulfates, trifluoroacetates,oxalates, naphthenates, nitrates and acetates.
 12. A process accordingto claim 11 wherein the oxidant salt compound is selected from the groupconsisting of copper (II) bromide, copper (I) iodide, copper (II)chloride, iron (II) iodide, iron (III) iodide, copper (II) sulfate, andcopper (II) acetate.
 13. A process according to claim 12 wherein theoxidant salt compound is copper (I) iodide.
 14. A process according toclaim 12 wherein the oxidant salt compound is copper (II) bromide.
 15. Aprocess according to claim 12 wherein the oxidant salt compound iscopper (II) chloride.
 16. A process according to claim 1 wherein theligand or coordination complex is lithium iodide.
 17. A processaccording to claim 1 wherein the ligand or coordination complex islithium bromide.
 18. A process according to claim 1 wherein the ligandor coordination complex is potassium or sodium iodide.
 19. A processaccording to claim 1 wherein the reaction is carried out in the presenceof a catalytic amount of from 0 to 20 weight percent based on thediolefin employed of a monohydric saturated aliphatic alcohol containingfrom 1 to 4 carbon atoms which may contain other substituents whichwould not interfere with the reaction.
 20. A process according to claim19 wherein the alcohol is methyl alcohol.
 21. A process according toclaim 19 wherein the alcohol is ethyl alcohol.
 22. A process for thepreparation of methyl penta-2,4-dienoate which comprises reacting1,3-butadiene with a mixture of carbon monoxide and oxygen and astoichiometric quantity of a dehydrating agent selected from the groupconsisting of acetals, ketals, carboxylic orthoesters,trialkylorthoborates and 1,1-dialkoxycycloalkanes, at a pressure ofbetween about 100 psig and 2000 psig and at a temperature in the rangeof from about 80° C. to 150° C. in the presence of an effective amountof a palladium metal salt compound and a copper (I) oxidant saltcompound.
 23. A process according to claim 22 wherein the dehydratingagent is 1,1-dimethoxycyclohexane, the palladium metal salt compound ispalladium (II) iodide, and the copper (I) oxidant salt compound iscopper (I) iodide.
 24. A process according to claim 23 wherein thereaction is carried out in the presence of a catalytic amount of lithiumiodide and a catalytic amount of methyl alcohol.